Evaporative emission (EVAP) system diagnostic leak detection tests that monitor fuel system pressure and/or vacuum have been used. EVAP diagnostic leak detection tests may be conducted during engine-off conditions because fuel system pressure disturbances, such as fuel slosh, arising from regular vehicle operation may be absent. A typical diagnostic leak detection test may seal the EVAP system by closing the canister vent valve (CVV) and then monitor changes in fuel system vacuum and/or pressure to determine system integrity when the engine is off. However, if refueling is started during an engine-off diagnostic leak detection test, the ensuing increase in fuel system pressure due to the dispensed fuel may confound the results of the diagnostic leak detection test. Furthermore, the buildup in fuel system pressure may prematurely shutoff the fuel dispensing pump.
Tomisawa (U.S. Pat. No. 5,542,394) discloses a vehicle engine refueling detection apparatus that detects a refueling event when the engine is off, and when a fuel tank pressure is greater than or equal to a predetermined value.
The inventors herein have recognized potential issues with the above approach. Namely, the method does not account for refueling during engine-off conditions when a diagnostic leak detection test is being performed. In particular, if the CVV (or another device that restricts fluid flow in the system) is closed to perform a diagnostic leak detection test, then an increase in fuel tank pressure due to a refueling event may be greater than when the CVV is open. Furthermore, if the fuel tank pressure signal is noisy, for example, due to a faulty sensor, a false refueling event may be detected.
One approach for at least partially addressing the aforementioned issues is a method of indicating a refueling event comprising during an engine-off condition, indicating a refueling event based on a rate of change in fuel tank pressure, and aborting a diagnostic leak detection test based on the refueling event indication. In particular, the refueling event indication may be based on the rate of change in fuel tank pressure being greater than a first threshold when the canister vent valve is open, and greater than a second rate of change in fuel tank pressure when the canister vent valve is closed, the first threshold being less than the second threshold. In this way, reliability in indicating a refueling event can be increased.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.